Synthesis and characterization of vinyltriethoxysilane-modified polycarboxylate superplasticiser for enhanced sulfate resistance

doi:10.21203/rs.3.rs-4914802/v1

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Synthesis and characterization of vinyltriethoxysilane-modified polycarboxylate superplasticiser for enhanced sulfate resistance

https://doi.org/10.21203/rs.3.rs-4914802/v1

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The strategic integration of functional monomers within the molecular structure of polycarboxylate superplasticizers offers a viable route to augment their inherent performance capabilities or introduce novel functionalities. In this investigation, a novel silane-modified polycarboxylate superplasticizer (Si-PCE) was synthesized via a free radical polymerization process at room temperature. This synthesis leveraged the high reactivity of ethylene glycol monoethylene glycol ether (EPEG), acrylic acid (AA), and vinyltriethoxysilane (VTEO) as the core monomers. The chemical structure of Si-PCE was characterized by Fourier transform infrared spectroscopy (FT-IR), ¹H Nuclear magnetic resonance (¹H NMR), and Energy dispersion spectroscopy (EDS). To evaluate the performance of Si-PCE, its influence on the early hydration products of cement was analyzed using X-ray Diffraction (XRD). Furthermore, the dispersibility of Si-PCE was assessed through cement paste fluidity and mortar fluidity tests, while its impact on mechanical property was investigated via mortar strength measurement. The findings revealed that Si-PCE surpassed silane-free PCEs in terms of dispersibility and dispersion retention, leading to enhanced mechanical property. In addition, the adaptability of Si-PCE in sulfate-rich environments was examined by conducting cement paste fluidity, mortar fluidity, and mortar compressive strength tests. Notably, Si-PCE demonstrated superior performance compared to its silane-free counterpart, particularly in high-sulfate environments, where it effectively dispersed cement particles and significantly bolstered the mechanical property of cement mortar. In conclusion, Si-PCE exhibited not only superior performance under conventional conditions but also remarkable adaptability and stability in sulfate-rich environments, thereby portending its extensive potential for application and profound implications.

polycarboxylate superplasticizer

silane

sulfate

EPEG

fluidity

Polycarboxylate-based superplasticizer (PCE) stands as the third-generation superplasticizer, succeeding lignosulfonate-based and naphthalene-based predecessors. Its prevalence in civil engineering stems from its exceptional abilities to disperse cement particles, minimize cement usage, and bolster the compressive strength of concrete ^[1–4]. PCE possesses a unique comb-like macromolecular structure, comprising a backbone and side chains. The backbone's moieties, predominantly carboxyl and sulfonic acid polar groups, adhere to the cement particle surfaces, imparting a uniform negative charge that disperses the particles through electrostatic repulsion. Meanwhile, the side chains, often composed of long-chain polyethers, extend into the aqueous phase, creating a substantial adsorption layer that induces a powerful steric repulsion, further enhancing dispersion ^[5–7]. Unlike conventional superplasticizers, PCE excels in its customizable molecular design. By incorporating diverse functional monomers into its molecular architecture, PCE can be tailored to enhance performance or acquire novel functionalities, enabling concrete formulated with these specialized PCEs to meet diverse application requirements ^[8–12].

Conventionally, the adsorption of PCE onto cement particles heavily relies on electrostatic physical adsorption. However, due to the inherent instability of this physical interaction, PCE tends to readily desorb from the cement surface, thereby compromising its dispersion performance. In contrast, chemical adsorption, facilitated by the formation of chemical bonds, possesses a stronger adsorption driving force and consequently enhances the dispersing ability of PCE on cement surfaces. Therefore, by strategically incorporating functional monomers capable of chemical adsorption into the molecular structure of PCE, the adsorption efficacy on cement can be improved, ultimately bolstering the dispersion properties of cement.

Silane coupling agents, as organic silicon compounds with a unique structure, possess the remarkable ability to react with both inorganic materials (such as glass, cement, metal, etc.) and organic materials (including fibers, resins, rubber, etc.). This versatility has led to their widespread application in the manufacturing of composite materials. Extensive research has been conducted to explore the influence of silane coupling agents on cement hydration, revealing that their direct addition to cement system can significantly enhance the performance of concrete ^[13–17]. For instance, Chen et al. ^[13] discovered that at an early stage, silanes act as retardants in cement paste due to the attractive forces between their intermediate hydrolysis products and cement hydrated products. Nonetheless, after 28 days of curing, the structure of silane-modified cement was observed to be more compact, exhibiting lower porosity, a higher degree of hydration, and superior mechanical properties compared to pure cement paste. Husillos-Rodríguez et al. ^[14] conducted a comprehensive study on the influence of silane on the initial hydration process in Portland cement pastes. Their findings also revealed that the introduction of silane significantly prolongs the induction phase of the cement paste, compared to the control sample. Notably, this effect became more pronounced as the concentration of silane increased. Casagrande et al. ^[15] further examined the mechanical properties of cement paste when partially replacing superplasticizer with various silanes, including tetraethoxysilane (TEOS), 3-glycidoxypropyltrimethoxysilane (GPTMS), and aminoethylaminopropyltrimethoxysilane (AEAPTMS). Their analysis showed that a 25% substitution with any of these silanes resulted in an enhanced mini-slump and a reduced air content in the pastes, in comparison to the reference. However, a 50% incorporation of GPTMS or AEAPTMS had contrasting effects, diminishing the mini slump and increasing the air content. In contrast, a similar 50% substitution with TEOS did not significantly alter these properties.

Drawing upon the distinctive reactivity of silane coupling agents and their capacity to enhance the performance of cement paste, researchers have diligently explored the integration of silane coupling agents into the molecular structure of PCE to augment their inherent performance capabilities or introduce novel functionalities ^[18–24]. Fan et al. ^[18] achieved the successful synthesis of various silane-modified PCEs through radical copolymerization in THF, revealing that these modified PCEs establish robust chemical bonds with calcium silicate hydrate, thereby augmenting their adsorption capacity on cement particle surfaces and enhancing PCE's resilience to sulfate ions. Similarly, Plank et al. ^[19] developed a facile synthesis protocol for silane-modified PCE in water, observing an augmentation in adsorption capability on cement particles, superior cement dispersibility, and reduced sensitivity to sulfate ions. This enhanced performance is attributed to the formation of chemical bonds between the silyl functionalities of the PCEs and the hydrated silicate phases of cement. Orozco et al. ^[20] further validated the establishment of covalent bonds through siloxane interactions between the silanol groups in silane-modified PCE and the unbound oxygen atoms in the dimeric structures of synthetic calcium silicate hydrate. Ma et al. ^[21] corroborated that silane-modified PCE adheres to cement particle surfaces through both chemical and electrostatic adsorption mechanisms, noting that the introduction of longer silane chains onto PCE diminishes its electrostatic adsorption. Notably, in the presence of silane-modified PCE with higher adsorbed quantities, cement pastes exhibit reduced yield stress, enhanced fluidity, and higher strength at 7 and 28 days. However, the precise correlation between silane monomer content and its dispersing effect on cement remains an area of ongoing research. A comprehensive investigation by Huang et al. ^[22] elucidated the intricate interplay between silane concentration and the compatibility of silane-modified PCE with silica fume (SF). Notably, it was ascertained that at reduced concentrations of methacryloxypropyl trimethoxysilane (MAPTMS), the silane-modified PCE exhibited superior dispersibility of silica fume compared to its unmodified counterpart. However, a marked decrement in the dispersive efficacy of silane-modified PCE was observed when the molar substitution of acrylic acid (AA) by MAPTMS exceeded 40%. In a parallel study, Wang et al. ^[23] delved into the influence of silane-modified PCE on the properties of concrete in clay-rich environments. Their meticulous research demonstrated that the silane-modified PCE effectively enhanced the dispersion of cement particles and retained fluidity, thus contributing favorably to the amelioration of concrete's mechanical properties. More recently, Huang et al. ^[24] introduced a dual-functional silane-modified PCE, serving as both a superplasticizer and an interfacial agent between fresh and hardened concrete. Endowed with highly reactive silane groups, this novel superplasticizer outperformed commercial PCE in terms of water reduction efficiency and fluidity retention. Furthermore, it fostered a robust interfacial bond between fresh and hardened concrete, as evidenced by a significant increase in the interfacial shear strength. The aforementioned research has unequivocally demonstrated that the strategic incorporation of silane coupling agents into the molecular architecture of PCE facilitates efficient chemical adsorption of PCE within cement paste. Notably, the employment of silane-modified PCE has been observed to substantially augment the mechanical properties of cement paste, while also exhibiting other exceptional performance. Consequently, the in-depth exploration of silane-modified PCE holds significant importance in advancing the field of concrete technology.

Polyether macromonomers constitute a fundamental component in the synthesis of PCE, and their reactivity is a critical determinant of the optimal synthesis conditions. Conventionally, the utilization of poly(ethylene glycol) methyl ether methacrylate (MPEG), isobutylene polyvinyl ether (HPEG), or methyl alkenyl polyoxyethylene ether (TPEG) as macromonomers for the preparation of PCE has been extensively employed ^[25–27]. However, their relatively low reactivity necessitates the application of high-temperature heating to effectively promote the free radical polymerization reaction. In recent years, ethylene glycol monovinyl polyether glycol (EPEG) has garnered attention as a novel polyether macromonomer exhibiting superior reactivity compared to the conventional macromonomers ^[28–30]. This elevated reactivity enables EPEG to undergo radical polymerization reactions efficiently, even at room temperature or under low-temperature conditions. As a result, the incorporation of EPEG as a macromonomer in the preparation of PCE offers the potential to lower the copolymerization temperature and enhance the efficiency of the polymerization reaction, ultimately resulting in reduced production costs.

In the present investigation, we have achieved the successful synthesis of a novel silane-modified PCE (Si-PCE) through the radical polymerization at room temperature. Specifically, the synthesis entailed the utilization of ethylene propylene glycol ether (EPEG), acrylic acid (AA), and vinyltriethoxysilane (VTEO) as the fundamental reactants. The resulting Si-PCE was then rigorously evaluated for its effectiveness in enhancing the dispersion performance of cement, which was assessed through cement paste fluidity and mortar fluidity tests. Additionally, the adaptability of the Si-PCE to sulfates was thoroughly investigated to determine its potential for application in sulfate-rich environments. This research provides valuable insights into the synthesis and properties of silane-modified PCE.

2.1. Raw Materials

EPEG (Mn = 3000, industrial grade) was supplied by Liaoning Kelong Fine Chemical Co., Ltd. VTEO (Industrial Grade) was provided by Hangzhou Jessica Chemical Co., Ltd. AA (analytically pure), ascorbic acid (Vc, analytically pure), Na₂SO₄ (analytically pure), and 3-mercaptopropionic acid (MPA, analytically pure) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. H₂O₂ (30 wt%, analytically pure) and NaOH (analytically pure) were obtained by Tianjin Guangcheng Chemical Reagent Co., Ltd. A dialysis bag (MD25-3500D) was purchased from Viskase (USA). Standard Portland cement (P·O 42.5) was produced by Shandong Shanshui Group Co., Ltd., and its chemical compositions are presented in Table 1. ISO standard sand was purchased from Xiamen Aisiou Standard Sand Co., Ltd.

Table 1

Chemical compositions of cement
Compositions	CaO	SiO₂	Al₂O₃	Fe₂O₃	MgO	SO₃
Mass (%)	52.12	22.68	8.94	3.27	4.79	2.36

2.2 Synthesis of Si-PCE

The synthesis of Si-PCE were carried out via free radical polymerization with EPEG, AA and VTEO as reactive monomers. H₂O₂ and Vc, serving as redox initiators, were initially added to the reaction mixture, followed by MPA as a chain transfer agent. The synthesis procedure was executed in a 250 mL three-neck flask equipped with a stirring apparatus and a thermometer. Initially, EPEG was dissolved in deionized water under stirring to ensure complete dissolution. Subsequently, H₂O₂ was added, and the mixture was stirred for 15 minutes to homogenize the initiator. Separately, two solutions were prepared: Solution A, containing AA, VTEO, and deionized water, and Solution B, comprising MPA, Vc, and deionized water. Both solutions were introduced dropwise into the reaction flask simultaneously under continuous stirring. After the complete addition of Solutions A and B, the reaction mixture was maintained under stirring for an additional 20 minutes. Finally, to neutralize the reaction mixture, a 30% aqueous solution of NaOH was cautiously added to adjust the pH of the reaction mixture to a neutral range (6–7). The synthesis route is schematically depicted in Fig. 1. The synthesis process for the silane-free PCE follows an identical sequence of steps as that of Si-PCE.

2.3. Structural characterization and testing methods

2.3.1 Fourier transform infrared spectroscopy (FT-IR)

FT-IR analysis was conducted using a Bruker TENSOR 27 instrument (Bruker, Germany) at 25°C within a wavenumber range of 400 to 4000 cm^− 1. Prior to the analysis, the sample was carefully packed into a dialysis bag and underwent a thorough dialysis process in deionized water. Subsequently, the dialyzed product was dried thoroughly in a vacuum oven.

2.3.2. ¹H nuclear magnetic resonance (¹H NMR)

The molecular structure of Si-PCE was determined employing the AVANCE II 400 MHz nuclear magnetic resonance spectrometer (Bruker, Germany). The deuterated water (D₂O) was utilized as the solvent, and tetramethylsilane (TMS) served as the internal standard.

2.3.3. Energy dispersion spectroscopy (EDS)

The Oxford Ultim Extreme EDS spectrometer (Oxford Instruments, UK) was employed to analyze the chemical compositions of Si-PCE.

2.3.4 Fluidity of cement paste

The fluidity of cement paste was evaluated in accordance with the Chinese national standard GB/T 8077 − 2012, Test Method for Uniformity of Concrete Admixtures. The water-to-cement ratio (W/C) was set at 0.29, and the addition of superplasticizer was controlled at 0.20%.

2.3.5 Fluidity of cement mortar

The fluidity of cement mortar was experimentally determined according to the Chinese national standard GB/T 8077 − 2012, Test Method for Uniformity of Concrete Admixtures. The superplasticizer content was maintained at 0.20%.

2.3.6 X-ray diffraction (XRD)

XRD analysis was conducted to obtain the diffraction patterns for phase analysis using a D8 Advance X-ray diffractometer. The instrument was operated at a current of 40 mA and a voltage of 40 kV, with a scanning speed of 1°/min and a 2θ range of 5°-40°.

2.3.7 Mechanical properties of cement mortar

The mechanical properties of cement mortar was evaluated according to the Chinese national standard GB/T 17671 − 2021, Cement mortar strength Testing Method (ISO method), with a W/C ratio of 0.45 and the addition of 0.20% superplasticizer.

3.1 Molecular structural characterization of Si-PCE

The molecular structure of Si-PCE was characterized using FT-IR, and the results are presented in Fig. 2. As observed in Fig. 2, characteristic absorption peaks corresponding to the EPEG and AA components are both discernible in the FT-IR spectrum of Si-PCE. Specifically, the peaks attributed to the symmetric stretching and bending vibrations of the -CH₂-CH₂-O- unit in the EPEG monomer are evident at 2886 cm^− 1 and 950 cm^− 1, respectively. Additionally, the asymmetric stretching vibration of the C-O-C bond appears at 1110 cm^− 1, while the C-H bending vibrations of the -CH₃ and -CH₂ groups are discernible at 1356 cm^− 1 and 1467 cm^− 1, respectively. Notably, the carboxyl acid group in AA exhibits a C = O vibration peak at 1580 cm^− 1, and the ester group's C = O bond stretching vibration is observed at 1726 cm^{− 1 [31]}. Importantly, the characteristic absorption peak of the C = C bond in EPEG, typically observed at 1670 cm^− 1, is absent in the Si-PCE spectrum. This significant absence indicates the absence of C = C bonds in the Si-PCE molecular structure, thereby confirming the successful polymerization between the reactive monomers. Based on these FT-IR findings, it can be preliminarily concluded that EPEG, AA, and VTEO have been successfully incorporated into the molecular structure of the polycarboxylate superplasticizer.

¹H NMR was employed to further elucidate the molecular structure of Si-PCE, and the results are presented in Fig. 3. In the spectrum of VTEO, the proton resonance at a chemical shift of δ = 1.0 ppm is characteristic of the methyl protons (-CH₃). The resonance at δ = 3.6 ppm corresponds to the protons present in the methylene (-CH₂-) groups, whereas the chemical shift range of δ = 5.5-6.0 ppm is representative of the vinyl protons (-CH = CH₂). In the EPEG spectrum, the chemical shift range at δ = 3.4–3.8 ppm is attributed to the protons in the ether linkage (-O-CH₂-CH₂-O-). The chemical shift range at δ = 4.0-4.2 ppm is indicative of the terminal vinyl protons (-CH = CH₂) in the EPEG molecule. Notably, in the Si-PCE spectrum, the chemical shifts ascribed to the vinyl protons of VTEO (δ = 5.5-6.0 ppm) and EPEG (δ = 4.0-4.2 ppm) are both absent. This observation is indicative of the successful radical polymerization reaction between the vinyl moieties of VTEO and EPEG. Furthermore, the disappearance of the methyl proton resonance at δ = 1.0 ppm, originally present in VTEO, implies the hydrolysis of the ethoxy groups (-O-CH₂-CH₃) during the synthesis. The combined ¹H NMR findings conclusively validate the incorporation of EPEG and VTEO into the polycarboxylate superplasticizer structure, thereby confirming the successful synthesis of the Si-PCE copolymer.

To ascertain the elemental compositions of the Si-PCE, an EDS analysis was conducted. The results are presented in Fig. 4 and Table 2. Notably, the mass fraction of silicon (Si) was determined to be 0.38%. This substantial proportion underscores the successful incorporation of the VTEO monomer into the molecular structure of the Si-PCE, thereby validating the effectiveness of the synthesis process.

Table 2

Elemental composition of Si-PCE
Element	C	O	Na	Si
Weight fraction (%)	70.58	19.84	8.55	0.38
Mole fraction (%)	78.14	16.49	4.95	0.18

3.2. Dispersibility of Si-PCE

To systematically explore the influence of the molar ratio between VTEO and AA on the fluidity of cement paste, a series of Si-PCEs were synthesized while maintaining all other reaction conditions constant and the overall molar ratio of reactant monomers consistently set at n_(VTEO+AA): n_(EPEG) = 4.5:1. Specifically, for the extreme case where n_(VTEO): n_(AA) = 0:4.5, the resulting product was a silane-free PCE. To evaluate the effect of varying the VTEO to AA molar ratio on the dispersing performance, a rigorous investigation was undertaken by analyzing the fluidity of cement paste. The outcomes of this analysis are presented in Fig. 5.

As evident from Fig. 5, as the concentration of VTEO within the Si-PCE increases within the range of 0 to 0.7, the fluidity of cement paste exhibits a progressive enhancement at various intervals, including initially, 30-minute, 60-minute, and 120-minute. Notably, the fluidity of cement paste achieved with Si-PCE significantly surpasses that attained using silane-free PCE over the course of time. Specifically, when the molar ratio of VTEO to AA is set at n_(VTEO):n_(AA) = 0.7:3.8, the fluidity of cement paste sustains a notable value of 220 mm even at 120-minute interval, whereas the corresponding value for silane-free PCE is significantly lower, at 89 mm. The dispersive effect of PCE on cement primarily originates from the electrostatic repulsion exerted by short-chain carboxyl groups and the steric hindrance provided by long-chain macromolecules. However, the introduction of silane into the molecular structure of PCE introduces a novel mechanism. The silanol groups generated through the hydrolysis of alkoxy groups in silane can form Si-O-Si chemical bonds with the hydroxyl groups present on the surface of cement particles, leading to chemical adsorption. This, in turn, further enhances the adsorption of the superplasticizer onto cement hydration products ^[32]. Consequently, as the silane content in the superplasticizer increases, the interaction between the Si-PCE and the cement hydration products intensifies, resulting in superior dispersion performance compared to silane-free PCE. Notably, Fig. 5 also highlights that upon a further increase in VTEO content to 0.8, the fluidity of cement paste drops sharply at all intervals, even below the values observed for silane-free PCE. This phenomenon can be attributed to the dual nature of silane groups within the Si-PCE molecular structure. While they can form chemical bonds with cement particles, the silane groups themselves are also prone to hydrolysis and condensation, leading to the formation of cross-linked structures. With an excessive proportion of silane, these groups condense to form polymers within the cement paste, thereby hindering the adsorption of the superplasticizer onto the cement particle surface. Therefore, the evaluation of cement paste fluidity underscores the criticality of determining an adequate molar ratio of VTEO in the molecular structure of Si-PCE, thereby enabling the complete realization of silane's functional role. This optimal ratio is essential for maximizing the dispersibility of the cement paste, ensuring the superior performance of the cement system.

To conduct a rigorous evaluation of the effects of VTEO on the dispersion efficacy of the superplasticizer, an analysis of the fluidity of cement mortar was undertaken, with the results presented in Fig. 6. As evident in Fig. 6(a), the cement mortar formulations incorporating Si-PCE, which was modified with VTEO, exhibited significantly higher fluidity compared to that with silane-free PCE, across the initial, 30-minute, and 60-minute intervals. Notably, the fluidity of the Si-PCE-mixed cement mortar sustained a remarkable value of 185 mm even after 60 minutes, in contrast the corresponding value for the silane-free PCE-mixed mortar exhibited a fluidity of 100 mm during the same time frame.

Figure 6(b) further reveals the differences in fluidity retention between the two formulations. Specifically, the silane-free PCE-based cement mortar exhibited fluidity loss rates of 31.8% and 55.2% at 30-minute and 60-minute intervals, respectively. In contrast, the Si-PCE formulations demonstrated substantially lower loss rates of 4.7% and 30.2% at the corresponding time intervals. This substantial difference underscores the remarkable fluidity retention capabilities of the Si-PCE. Consequently, these findings unequivocally confirm that the incorporation of VTEO into PCE significantly enhances the dispersion performance and retention of cement, thus contributing to superior workability and durability of cement-based materials.

3.3. Cement hydration products

During the hydration of tricalcium silicate (C₃S) and dicalcium silicate (C₂S) in cement, a significant quantity of crystals emerges, encompassing both gel-forming substances and Ca(OH)₂ crystals. These crystal species serve as indicators for evaluating the extent of cement hydration, as their quantitative production directly correlates with the degree of hydration.

To investigate the effects of Si-PCE on the development of hydration products, XRD analysis was conducted. As depicted in Fig. 7, the characteristic diffraction peak of ettringite (AFt), a hydration product, is observed at a diffraction angle 2θ of 9.1°, whereas the peak corresponding to Ca(OH)₂, another hydration product, manifests at 2θ of 18°. For cement pastes containing Si-PCE, both the intensities of the Ca(OH)₂ and AFt peaks are observed to be heightened compared to those in the silane-free PCE cement pastes at hydration durations of 1 and 3 days. This phenomenon suggests that the incorporation of Si-PCE enhances the hydration kinetics of cement. Specifically, the silanol groups generated through the hydrolysis of silane in Si-PCE chemically interact with the hydroxyl groups on the cement surface, thereby improving the dispersion of cement particles. This interaction facilitates an accelerated initial hydration phase and leads to a shorter cement hydration induction period.

3.4. Compressive strength of mortar

The effects of Si-PCE on the mechanical properties of cement mortar were evaluated through compressive strength testing. The compressive strengths of the specimens were measured at 3, 7, and 28 days of curing. As depicted in Fig. 8, the incorporation of Si-PCE resulted in higher compressive strengths compared to those specimens containing a silane-free PCE, at all curing ages. Prior studies on the fluidity of cement paste and mortar have established that the inclusion of Si-PCE enhances the dispersion performance of cement particles, thereby promoting an increase in cement hydration products. This improved dispersion performance contributes to a denser microstructure of the samples, ultimately leading to an augmentation in their compressive strength.

3.5 Adaptability of Si-PCE to sulfate

In the context of cementitious materials, the inclusion of sulfates, originating from various sources such as cement, and other admixtures, poses a significant challenge to the performance of superplasticizers. The presence of sulfates can compete with superplasticizers for adsorption sites on the surface of cement particles, potentially diminishing the dispersion performance of the superplasticizer and having adverse implications on the overall performance of cement concrete ^[33]. Therefore, it is crucial to examine the adaptability of Si-PCE to sulfate environments.

3.5.1 Dispersibility of Si-PCE in sulfate environments

The adaptability of Si-PCE to sulfates was investigated through cement paste fluidity test. As depicted in Fig. 9, the results indicate that when the dosage of Na₂SO₄ is set at 0.2%, the fluidity of cement paste incorporating Si-PCE is notably superior to that containing silane-free PCE at all measured intervals. Remarkably, even when the dosage of Na₂SO₄ is increased to 0.4%, the cement paste formulated with Si-PCE still exhibits superior fluidity compared to silane-free PCE. This superiority is attributed to the unique ability of Si-PCE to form chemical adsorption bonds on the surface of cement particles. In the initial stages of cement hydration, Si-PCE can rapidly adsorb onto cement particles and hydration products, generating a robust adsorption force that is resilient to the competitive adsorption of sulfates. Consequently, Si-PCE demonstrates reduced sensitivity to sulfates and superior dispersion properties.

3.5.2. Effect of sulfate on the compressive strength

Under the conditions with a W/C ratio of 0.4 and a superplastizer dosage of 0.2%, the effect of sulfates on the compressive strength of cement mortar enhanced with Si-PCE was investigated. As depicted in Fig. 10, when the dosage of Na₂SO₄ is set at 0.2%, the compressive strength of cement mortar containing Si-PCE outperforms that of silane-free PCE-based mortar at 3, 7, and 28 days. Moreover, as the Na₂SO₄ dosage escalates to 0.4%, the compressive strength of Si-PCE-based cement mortar exhibits remarkable gains of 25%, 42%, and 53% over silane-free PCE-based mortar at 3, 7, and 28 days, respectively. Notably, the 28-day compressive strength of Si-PCE-based cement mortar attains a significant value of 43.2 MPa, significantly surpassing the 28.3 MPa achieved by silane-free PCE-based mortar. In a sulfate-rich environment, the presence of sulfates introduces a competitive adsorption mechanism with PCE on the surface of cement particles, leading to a decrease in PCE adsorption. This phenomenon is exacerbated at higher sulfate concentrations, potentially causing desorption of PCE and consequently diminishing the dispersibility of the cement paste. Conversely, Si-PCE exhibits a robust dual adsorption mechanism, encompassing both physical and chemical interactions, on the cement particle surface. This attribute ensures a more stable adsorption of Si-PCE, enhancing dispersion performance and ultimately resulting in superior mechanical strength.

In this research, a novel series of silane-modified PCEs were successfully synthesized via a free radical copolymerization process. This product leverages the complementary advantages of polycarboxylate superplasticizers and silane modification, imparting exceptional dispersibility and stability in cement system. A comprehensive investigation was undertaken to evaluate the dispersion characteristics, mechanical properties, and sulfate resistance of cement slurries doped with the synthesized Si-PCE. The main conclusions are summarized as follows:

(1) A novel silane-modified PCE was successfully synthesized through a free radical polymerization process, involving the copolymerization of AA and VTEO in the presence of a highly reactive polyether macromonomer, EPEG, at ambient temperature.

(2) The dispersion properties of the Si-PCE were significantly superior to those of silane-free PCE. The optimization of the dispersion performance was achieved by fine-tuning the molar ratio of the reactive monomers. Specifically, at a monomer ratio of n(VTEO): n(AA) = 0.7:3.8, the Si-PCE exhibited the most effective dispersion performance for cement. This optimal formulation resulted in an initial cement paste fluidity of 320 mm, which was sustained at 220 mm even after 120 minutes. Hence, the inclusion of an appropriate molar ratio of VTEO in the Si-PCE formulation is crucial to fully harness the benefits of silane modification.

(3) The XRD analysis revealed that the Si-PCE effectively promotes the early hydration of cement and significantly shortens its hydration induction period. Additionally, compressive strength tests have indicated that the enhanced dispersion properties of the Si-PCE led to an increase in the compressive strength of cement mortar.

(4) The Si-PCE exhibited robust adaptability to sulfate environments, enhancing the fluidity of cement paste in sulfate-rich conditions and significantly improving the compressive strength of the corresponding cement mortars. Specifically, when the sulfate content was increased to 0.4%, the 3-day, 7-day, and 28-day compressive strengths of cement mortars containing the Si-PCE increased by 25%, 42%, and 53%, respectively, compared to those containing the silane-free PCE.

Author contributions

Yuxia Gao: Investigation, Writing-Original draft preparation. Fuying Dong: Supervision, Conceptualization, Methodology, Writing-Reviewing and Editing. Tongxin Guo: Investigation, Experiment. Jianqin Wang: Investigation, Experiment. Qiuting Chu: Methodology. Fulong Li: Investigation, Experiment. Xiao Yang: Experiment, Investigation. Xinde Tang: Conceptualization. Laixue Pang: Investigation. Kun Wang: Investigation. Peng Hu: Investigation. Rui Kuang: Investigation. All authors have read and agreed to the published version of the manuscript.

Acknowledgements

The authors thank the financial support by Shandong Provincial Natural Science Foundation of China (Grant No.ZR2022ME135) and the National Undergraduate Innovation and Entrepreneurship Training Plan.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Declaration of Interest Statement

All authors declare that no conflict of interest exists.

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You are reading this latest preprint version

Synthesis and characterization of vinyltriethoxysilane-modified polycarboxylate superplasticiser for enhanced sulfate resistance

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Raw Materials

2.2 Synthesis of Si-PCE

2.3. Structural characterization and testing methods

2.3.1 Fourier transform infrared spectroscopy (FT-IR)

2.3.2. ¹H nuclear magnetic resonance (¹H NMR)

2.3.3. Energy dispersion spectroscopy (EDS)

2.3.4 Fluidity of cement paste

2.3.5 Fluidity of cement mortar

2.3.6 X-ray diffraction (XRD)

2.3.7 Mechanical properties of cement mortar

3. Results and discussion

3.1 Molecular structural characterization of Si-PCE

3.2. Dispersibility of Si-PCE

3.3. Cement hydration products

3.4. Compressive strength of mortar

3.5 Adaptability of Si-PCE to sulfate

3.5.1 Dispersibility of Si-PCE in sulfate environments

3.5.2. Effect of sulfate on the compressive strength

4. Conclusions

Declarations

References

Additional Declarations

Status:

Version 1

Synthesis and characterization of vinyltriethoxysilane-modified polycarboxylate superplasticiser for enhanced sulfate resistance

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Raw Materials

2.2 Synthesis of Si-PCE

2.3. Structural characterization and testing methods

2.3.1 Fourier transform infrared spectroscopy (FT-IR)

2.3.2. 1H nuclear magnetic resonance (1H NMR)

2.3.3. Energy dispersion spectroscopy (EDS)

2.3.4 Fluidity of cement paste

2.3.5 Fluidity of cement mortar

2.3.6 X-ray diffraction (XRD)

2.3.7 Mechanical properties of cement mortar

3. Results and discussion

3.1 Molecular structural characterization of Si-PCE

3.2. Dispersibility of Si-PCE

3.3. Cement hydration products

3.4. Compressive strength of mortar

3.5 Adaptability of Si-PCE to sulfate

3.5.1 Dispersibility of Si-PCE in sulfate environments

3.5.2. Effect of sulfate on the compressive strength

4. Conclusions

Declarations

References

Additional Declarations

Status:

Version 1

2.3.2. ¹H nuclear magnetic resonance (¹H NMR)